* Corresponding author. E-mail address: b.zeynizadeh@urmia.ac.ir (B. Zeynizadeh) © 2020 Growing Science Ltd. All rights reserved. doi: 10.5267/j.ccl.2019.12.001 Current Chemistry Letters 9 (2020) 121–130 Contents lists available at GrowingScience Current Chemistry Letters homepage: www.GrowingScience.com Highly efficient method for oximation of aldehydes in the presence of bis-thiourea complexes of cobalt, nickel, copper and zinc chlorides Behzad Zeynizadeh a* and Serve Sorkhabi a a Faculty of Chemistry, Urmia University, Urmia 5756151818, Iran C H R O N I C L E A B S T R A C T Article history: Received June 21, 2019 Received in revised form December 8, 2019 Accepted December 8, 2019 Available online December 8, 2019 In this study, the selective oximation of structurally diverse aromatic aldehydes (versus ketones) to the corresponding aldoxime derivatives was investigated using the combination system of NH2OH·HCl and bis-thiourea complexes of cobalt, nickel, copper and zinc chlorides, M II (tu)2Cl2, in a mixture of CH3CN-H2O (1:1). All reactions were carried out successfully at room temperature within the immediate time up to 130 min giving the products in high yields. Investigation of the results exhibited that the applied bis-thiourea metal complexes represented the catalytic activity in order of Co(tu)2Cl2> Ni(tu)2Cl2> Cu(tu)2Cl2> Zn(tu)2Cl2 in their oximation reactions. © 2020 Growing Science Ltd. All rights reserved. Keywords: Aldehydes Aldoximes M II (tu)2Cl2 NH2OH·HCl Oximation 1. Introduction Aldoximes and ketoximes are valuable chemical intermediates that are widely utilized in the chemical industry. 1,2 They are usually prepared by the reaction of carbonyl compounds and hydroxylamine hydrochloride in the presence of acids or bases including sulfuric acid 3 , formic acid 4 , pyridine 5 , sodium acetate and sodium hydroxide. 6,7 Because of some limitations such as low yield of the products, long reaction times and the presence of acid or base sensitive functionalities in aldehyde or ketonic compounds, the classical methods usually are not suitable. In this context, several improvements such as using nano Fe3O4 8 , Cu-SiO2 9 , NH2OH·HCl/K2CO3 10 , Dowex 50WX4 11 , hetero- geneous polyoxometalates 12,13 , phase transfer catalysts 14 , basic ionic liquid 1-butyl-3-methyl- imidazolium hydroxide 15 , NH3/oxidant/catalyst systems 16-21 , wet basic Al2O3/microwave 22 , SiO2/ NH2OH/microwave 23 , absence of any catalyst and solvent 24 , CaO/solvent-free 25 , TiO2/SO4 2 − solid super acid 26 , ethylenediamine/oxone 27 , Na2SO4/ultrasound 28 , titanyl acetylacetonate/NH2OH 29 , Bi2O3/ NH2OH·HCl 30 , clay-based titanium silicalite-1 31 , host (dealuminated zeolite Y)-guest (12-molybdo-